A cylinder head of a four-cycle engine is, like a cylinder block, directly exposed to combustion gas at a high temperature and a high pressure, and receives a high gas pressure and thermal load. Accordingly, the cylinder head requires characteristics closer to those needed in a cylinder block, and the cylinder heads are often manufactured of cast iron like the cylinder block. But different from the cylinder block, the cylinder head receives a larger amount of heat because the combustion of the mixed gas finishes near the top dead center of the piston, and it has no sliding part with the piston. Cylinder heads made of a lightweight aluminum alloy molding with a superior heat releasing property are therefore mainly used.
One known cylinder head is disclosed in Japanese Patent Publication No. 49-15162. The reciprocating internal combustion engine disclosed in this publication employs an oscillating action for the exhaust valve requiring less severity and a direct cam action for the intake valve to realize an overhead cam shaft apparatus with a high degree of freedom in design.
Another cylinder head is disclosed in Japanese Laid-Open Patent No. 58-135309. The hemispherical combustion chamber cross flow V-type valve configuration center spark plug SOHC engine disclosed in this publication possesses two cams on one cam shaft and the exhaust valve is opened and closed by one cam and the intake valve is opened and closed by the other cam through a rocker arm.
Still another cylinder head is disclosed in Japanese Laid-Open Utility Model No. 52-145207. The hydraulic controller for automatic valve clearance regulator in the valve operating system of the internal combustion engine disclosed in this publication is designed to open a bubble separating slot near the apex of the hydraulic chamber, to connect the bubble separating slot to a relief passage, and to mount a relief valve between the hydraulic chamber and the relief passage, thereby feeding a specific hydraulic pressure without containing bubbles to the valve clearance regulator.
In cylinder heads of the conventional four-cycle engine, exclusive cylinder heads are manufactured for each kind of engine including those using one cam and a pair of intake and exhaust valves (called 1-cam 2-valve engines), those using one cam and two pairs of intake and exhaust valves (called 1-cam 4-valve engines), and those using two cams and two pairs of intake and exhaust valves (called 2-cam 4-valve engines), and exclusive machining apparatus and exclusive parts were provided for each cylinder head.
Accordingly, the manufacturing cost of exclusive machining apparatus and exclusive parts for each cylinder head are enormous, and such system are economically not advantageous.
In addition, as the exclusive parts require checking and testing respectively, the developing period is consequently prolonged, the developing period can not be shortened, a large amount of developing cost is spent and a great deal of effort is needed, and therefore such system is economically and practically not advantageous.
The cylinder heads disclosed in Japanese Patent Publication No. 49-15162, in Japanese Laid-Open Patent No. 58-135309 and in Japanese Laid-Open Utility Model No. 52-145207 were designed without the aim of common use of the machining apparatus and components.
It is hence a primary object of this invention to provide cylinder heads for four-cycle engines not only economically advantageous so as to permit reducing the manufacturing cost, but also economically and practically advantageous by not requiring checking and testing for each type of part, by being capable of shortening the development period, and by being capable of reducing the period and effort for development by designing common machining apparatus and parts.